Time to weed the (EBM-)pyramids?!

26092008

Information overload is a major barrier in finding that particular medical information you’re really looking for. Search- and EBM-pyramids are designed as a (search) guidance both for physicians, med students and information specialists. Pyramids can be very handy to get a quick overview of which sources to use and which evidence to look for in which order.

But look at the small collection of pyramids I retrieved from Internet plus the ones I made myself (8,9)………

ALL DIFFERENT!!!!

What may be particularly confusing is that these pyramids serve different goals. As pyramids look alike (they are all pyramids) this may not be directly obvious.

There are 3 main kinds of pyramids (or hierarchies):

Search Pyramid (no true example, 4, 5 and 6 come closest)Guiding searches to answer a clinical question as promptly as possible. Begin with the easiest/richest source, for instance UpToDate, Harrison’s (books), local hospital protocols or useful websites. Search aggregate evidence respectively the best original studies if answer isn’t found or doubtful.

Pyramid of EBM-sources (3 ,4, 8 )
Begin with the richest source of aggregate (pre-filtered) evidence and decline in order to to decrease the number needed to read: there are less EBM guidelines than there are Systematic Reviews and (certainly) individual papers.

Pyramid of EBM-levels (1, 2, 5, 7, 9)
Begin to look for the original papers with the highest level of evidence.
Often only individual papers/original research, including Systematic Reviews, are considered (1, 9), but sometimes the pyramid is a mixture of original and aggregated literature (2,5)

A mixture of 2, 3 and/or 4 (2,5)

Further discrepancies:

Hierarchies.

Some place Cochrane Systematic Reviews higher than ‘other systematic reviews’, others place meta-analysis above Systematic reviews (2,6). This is respectively unnecessary or wrong. (Come back to that in another post).

Sometimes Systematic reviews are on top, sometimes Systems (never found out what that is), sometimes meta-analysis or Evidence based Guidelines

UpToDate is sometimes placed at the top of the pyramid in Summaries (4) OR at the base in Textbooks (5), where I think it should belong in terms of evidence levels, but not in terms of usefulness.

DARE is considered a review, but it is really a synopsis (critical appraised summary) of a Systematic Review.

Isn’t it about time to weed the pyramids rigorously?

Are pyramids really serving the aim of making it easier for the meds to find their information?

Like to hear your thoughts about this.

What my thoughts are? I will give a hint: I would rather guide the informationseeker through different routes, dependent on his background, question, available time and goal. The pyramid of evidence sources and the levels of evidence would just be part of that scheme, ideally.

I am a Senior Registrar in Psychiatry in Ardee, Co Louth, Ireland (essentially a senior registrar is a sort of senior resident) For a long time, i’ve been mulling over some of the ideas you’ve mentioned here. What concerns me is that pyramids do not capture the complexity of evidence, and of clinically useful evidence. Its well documented that studies of effectiveness may not have the methodological rigour of studies of efficacy, but that very rigour may limit the applicability of studies. Also, much clinically useful information (for instance H Pylori’s identification) comes originally from studies way down the pyramid, and if pyramids are used to teach medical students that everything that isn’t an RCT is useless, this may be missed.

maybe it isn’t so much time to weed the pyramid as to consider another shape?

[…] an evidence pyramid (because they aggregate individual studies, represented by the lowest layer). There are confusingly many pyramids, however [8] with different kinds of hierarchies and based on different […]

Hi Laika,
May I have permission to reformat your #9 chart into a pyramid for use? It’s a great recap of the levels of evidence for my reps when speaking with clinicians. It would be formatted into a pyramid and used as a discussion tool. Please let me know – thank you!

I am trying to create a small lesson to go along with a beginning journal club for my labor and delivery department. I love figure number 7 because it has 7 layers that coincide with our system wide epb council and shows filtered from nonfiltered sources of evidence. Is there any way I can print this out for handouts?